Sealing hollow structures
A method of sealing a hole in a wall of a hollow structure comprises providing a sealed chamber that is external to the structure and that is in fluid communication with an internal space of the structure via the hole. The structure may be a pipe-in-pipe structure and the internal space may be an annulus between outer and inner pipes. Fluid flows through the hole into or out of the chamber as the pressure and/or composition of fluid in the internal space is adjusted. Then, a plug is spun and friction-welded into the hole. The plug is inserted into the hole from within the chamber.
1. A method of sealing a hole in a wall of a hollow structure, the method comprising:
providing a sealed chamber that is external to the structure and that is in fluid communication with an internal space of the structure via the hole;
adding a housing defining a sealed auxiliary volume to the chamber, the auxiliary volume containing a welding machine that is arranged to spin a plug;
opening a sealed partition between the chamber and the auxiliary volume to form a sealed enclosure that comprises the chamber and the auxiliary volume in fluid communication with each other;
causing fluid to flow through the hole into or out of the sealed enclosure to adjust the pressure and/or composition of fluid in the internal space; and
friction welding a spinning plug into the hole, the plug being inserted into the hole from within the sealed enclosure.
2. The method of claim 1 , performed on a structure in the form of a pipe.
3. The method of claim 2 , comprising advancing the plug into the hole along a spin axis that is substantially aligned with a central longitudinal axis of the pipe.
4. The method of claim 2 , wherein the pipe is an outer pipe of a pipe in pipe structure and the internal space is an annulus between the outer pipe and an inner pipe.
5. The method of claim 1 , comprising maintaining the pressure and/or composition of the fluid in the internal space and in the chamber while friction welding the plug into the hole.
6. The method of claim 1 , further comprising removing the chamber from the structure and then removing a part of the plug that protrudes from the structure.
7. The method of claim 1 , wherein the chamber contains a welding machine that is arranged to spin the plug.
8. The method of claim 1 , comprising advancing the plug from the auxiliary volume, past the open partition and through the chamber for insertion into the hole.
9. The method of claim 1 , comprising removing the chamber and the auxiliary volume together from the structure after welding the plug into the hole.
10. The method of claim 1 , wherein the chamber is defined by an external fitting that is sealed to the structure surrounding the hole.
11. The method of claim 10 , comprising strapping the fitting to the structure and applying tension to pull the fitting against the structure.
12. The method of claim 1 , comprising friction welding the plug into the hole when the pressure and/or composition of fluid in the internal space reaches a predetermined threshold.